Lavender should ideally not be pruned unless dead wood removal or a light dead-heading is needed. They are very sensitive about soil drainage, so must not stay too wet at any point (but especially during winter), and often potting mix in containers drains better than in-ground planting beds. (Though a raised bed is a good compromise.) If you use a saucer under the pot, make sure it's either not used while the plant is outside to keep the pot's drain holes unobstructed or check it promptly after watering or rain so you can empty any accumulated water so it doesn't soak back into the soil and over-saturate the roots.

Perennial plants spending the winter in containers are at elevated risk of root damage, because their root balls are less insulated than they would be in the ground. They will experience both greater temperature swings overall but also will dry out faster than in-ground plants. Having said that, keeping species that can't handle soggy soil in a pot for the winter might be worth the risk of exposure to multiple freeze-thaw cycles since a container could at least allow its roots to dry out faster after heavy rain or a normal watering.

There is no one right way to overwinter lavender in Maryland; some years, the weather is just too wet for their tolerances and even long-established plants can decline or die, so you may need to just decide which scenario (potted or planted in-ground) is easiest for you to work with. If you decide to plant it in the ground, do so within the next month so it has time to establish some roots before the soil cools. If you keep it in a pot, nothing special needs to be done to prepare it for winter. Covering the pot as a way to insulate it won't be very beneficial, though you could place it in an area against a building where it won't warm-up too quickly or face the brunt of the chilling winter winds.

Miri